We are studying the immunoglobulin isotype switch induced by interleukins -4, -10 and -13 in B lymphocytes, focusing on the events at the DNA level. We previously developed a sensitive semiquantitative assay for IL-4-induced murine switch recombination to the immunoglobulin gamma1 gene, and have more recently re-engineered the strategy to demonstrate changes in the recombination to gamma3 and alpha induced by the lymphokine IL-10. We have also studied the effect of this lymphokine on switching of human tonsillar B cells; in this case we were able to demonstrate that the cytokine acts as a switch factor, as it increased the production of gamma-mu reciprocal products which represent a reliable marker for switch recombination. The assay for human gamma-mu reciprocal products has also been useful for identifying subpopulations of germinal center cells that appear to be enriched for isotype switching. To ascertain whether switch factors such as IL-4 act through DNA elements other than the known motifs in promoters upstream of each immunoglobulin heavy chain constant region, we have been trying to locate an expected human homolog of the locus control element that has been identified in mouse lying downstream of the C-alpha gene; when this region is identified, it will be examined for cytokine response elements. In addition, we are continuing our efforts to detect other potential targets of cytokines in isotype switching by examining effects of IL-4 on switch recombination of artificial recombination substrates transfected into B cells competent for switching. An additional study of the contribution of EBV infection to switching to IgE expression in humans is continuing. In collaboration with Drs. Zelazowski and Snapper, we are examining the role of the important B cell regulatory protein BSAP in cytokine-induced switching. Finally we are initiating studies to examine the extent to which IL-4-induced isotype switching can explain side effects of recombinant human IL-4 currently in Phase 2 clinical trials. Burd PR, Thompson WC, Max EE, Mills FC. J Exp Med 1995;181:1373-80. Carayannopoulos L, Max EE, Capra JD. Proc Natl Acad Sci U S A 1994;91:8348-52. Max EE, Jahan N, Yi H, McBride WO. Mol Immunol 1994;31:1029-36. Max EE, Wakatsuki Y, Neurath MF, Strober W. Curr Top Microbiol Immunol 1995;194:449-58. Neurath MF, Max EE, Strober W. Proc Natl Acad Sci U S A 1995;92:5336-40. Saxon A, Max EE, Diaz SD, Zhang K. Int Arch Allergy Immunol 1995;107:45-7. Wakatsuki Y, Neurath MF, Max EE, Strober W. J Exp Med 1994;179:1099-108. Zhang K, Max EE, Cheah HK, Saxon A. J Biol Chem 1994;269:456-462. Mills FC, Mitchell MP, Harindranath H, Max EE. J Immunology 1995;155:3021-36.